Analog comparators are utilized to compare a high-speed differential input signal (e.g., up to 10 Gb/s) to thresholds (e.g., positive and negative) and generate positive or negative signals when the input signal is greater than or less than the positive or negative thresholds respectively. The analog comparators are used as front-end of signal detection circuit and error-generation circuits in high-speed serial link receivers.
FIG. 1 illustrates example input and output waveforms of an analog comparator to demonstrate the functionality thereof. The input is a differential signal (VIN+−VIN−) that varies over time. The differential signal is compared to a threshold voltage (VTH). When the differential signal crosses over (exceeds) a positive threshold voltage (VTH+) a positive output signal (VOUT+) is generated and when the differential signal crosses over (is less than) a negative threshold voltage (VTH−) a negative output signal (VOUT−) is generated.
The analog comparator may utilize a common mode logic (CML) amplifier to determine when the differential signal exceeds the threshold voltage. The threshold voltage may be dependent on process, voltage, and temperature (PVT) variations. Any variations in the threshold voltage may affect the detection of the differential signal reaching the thresholds and accordingly may affect the timing and/or occurrence of the output signals. Such variations in output signals may affect applications where a fine signal detection level is required.